I think Steve may be right with the Amana connection....like everything else, it all comes down to money. Pre-Amana, you had some professional golfers such as Hogan and Snead wearing hats, but not caps, and without logos on them. Amana, with their big, puffed up, white caps with HUGE logos, blazed a trail. Before them, most pros went without hats...think Palmer and Nicklaus in the 60s and 70s.
Back in the early 70s, my Dad was the tournament chairman of the Iowa section of the PGA. He set about looking for sponsors to sweeten the purses of their club pro tournaments, and approached Amana, an Iowa-based company. They said sure, they'd kick in some money for the Section Championship, effectively doubling the purse, if ALL the pros competing wore Amana hats during the tournament. When my Dad took this proposal to the section members, he had a HUGE fight on his hands, as all the smooth, sophisticated Iowa club pros in their plaid sansabelts and pointy collars did NOT want to have a big white puffy cap messing up their bubble perm! Eventually, like on tour, money talked and they relented.
I wonder how much a genuine 1970s era Amana cap goes for on e-bay these days?